The polyphagous shot hole borer (PSHB), Euwallacea sp. nov fornicatus is an invasive beetle that vectors a disease called Fusarium dieback (FD). The disease stops the flow of water and nutrients in over 45 susceptible tree species, which can lead to the death of individual branches or, in severe cases, the entire tree. It is caused by the fungi that the beetle farm in their gallery as a food source: Fusarium euwallaceae, Graphium euwallaceae, and Paracremonium pembeum. PSHB attacks a wide variety of host species. The beetles bore tunnels (galleries) in which to lay their eggs and grow the fungi. A closely related Euwallacea species, the Kuroshio shot hole borer (KSHB), has been detected throughout Orange and San Diego Counties. Morphologically identical to PSHB, it also spreads a fungal disease caused by other species of Fusarium and Graphium.

In 2003, a single PSHB beetle was caught in a CDFA trap in Long Beach. The beetle went unnoticed until 2012 when it was found damaging backyard avocado and urban forest trees in the Los Angeles basin. A rapid monitoring response uncovered the broad host range of the pest-disease complex, but its ability to establish in native vegetation was only gradually recognized.

At these early stages of the epidemic, preventative and containment measures can fortunately be effective, providing adequate, rapid assessment of key landscape factors. At present, knowing which management approaches are more effective is limited by the lack of data on how the pest-disease complex spreads across a complex landscape. Monitoring efforts have recently focused on avocado groves (due to immediate investment in research and development by the agricultural industry), but have now expanded to include the broader landscape to allow for regional planning and land management that will reduce or manage this threat within southern California. — by Shannon Lynch and Akif Eskalen, University of California, Riverside (Lynch) and Santa Cruz (Eskalen)

For updates and more information, please visit our lab at www.eskalenlab.ucr.edu.